OBJECTIVE The influence of the Ramadan fasting on blood pressure (BP) in patients taking diuretics therapy has not been addressed specifically yet. The aim of this study was to examine the effect of long Ramadan fasting on BP with ambulatory BP monitoring in hypertensive patients using diuretics. METHODS This prospective, observational study was done on 129 hypertensive patients and was carried out in two groups: 73 treated hypertensive patients were assigned to the diuretic group and 56 treated hypertensive patients were allocated to the non-diuretic group. Twenty-four-hour ambulatory BP monitoring was performed during and after Ramadan. Mean overall, daytime and nighttime BP were measured and compared in both groups. The differences in mean SBP and DBP were recorded between the two monitoring periods. RESULTS In diuretic group, 24-h SBP decreased from 128.2 ± 17.9 to 119.3 ± 9.5 mmHg during Ramadan (8.9 units; P < 0.001). DBP decreased from 79.4 ± 10.9 to 75.3 ± 7.6 mmHg (4.1 units; P < 0.001). On the other hand, SBP and DBP were lower insignificantly in the non-diuretic group. The reduction in SBP was significantly higher in the diuretic group (overall: P = 0.005, daytime: P = 0.011, nighttime: P = 0.022). Thiazide-like diuretics lowered BP more than thiazide-type diuretic despite an insignificant difference. CONCLUSIONS This study suggested that Ramadan fasting might cause significant reductions in mean SBP and DBP measurements in patients using diuretics. Despite decreasing in BP, diuretics generally well tolerated and can be safe in well-controlled hypertensive patients during Ramadan fasting.